Can't find the 'libpq-fe.h header when trying to install pg gem

Question

I am using the Ruby on Rails 3.1 pre version. I like to use PostgreSQL, but the problem is installing the pg gem. It gives me the following error:

Answer 1

On Mac OS X run like this:

gem install pg -- --with-pg-config=***/path/to/pg_config***

***/path/to/pg_config*** is path to pg_config